diff --git a/clients/drcachesim/simulator/snoop_filter.cpp b/clients/drcachesim/simulator/snoop_filter.cpp
index 27db152bac3..c56f099aa22 100644
--- a/clients/drcachesim/simulator/snoop_filter.cpp
+++ b/clients/drcachesim/simulator/snoop_filter.cpp
@@ -74,14 +74,8 @@ void
 snoop_filter_t::snoop(addr_t tag, int id, bool is_write)
 {
     coherence_table_entry_t *coherence_entry = &coherence_table_[tag];
-    // Initialize new snoop filter entry.
-    if (coherence_entry->sharers.empty()) {
-        coherence_entry->sharers.resize(num_snooped_caches_, false);
-        coherence_entry->dirty = false;
-    }
 
-    auto num_sharers = std::count(coherence_entry->sharers.begin(),
-                                  coherence_entry->sharers.end(), true);
+    size_t num_sharers = coherence_entry->sharers.size();
 
     // Check that cache id is valid.
     assert(id >= 0 && id < num_snooped_caches_);
@@ -91,7 +85,8 @@ snoop_filter_t::snoop(addr_t tag, int id, bool is_write)
     assert(!coherence_entry->dirty || num_sharers == 1);
 
     // Check if this request causes a writeback.
-    if (!coherence_entry->sharers[id] && coherence_entry->dirty) {
+    if (coherence_entry->sharers.find(id) == coherence_entry->sharers.end() &&
+        coherence_entry->dirty) {
         num_writebacks_++;
         coherence_entry->dirty = false;
     }
@@ -101,16 +96,18 @@ snoop_filter_t::snoop(addr_t tag, int id, bool is_write)
         coherence_entry->dirty = true;
         if (num_sharers > 0) {
             // Writes will invalidate other caches_.
-            for (int i = 0; i < num_snooped_caches_; i++) {
-                if (coherence_entry->sharers[i] && id != i) {
-                    caches_[i]->invalidate(tag, INVALIDATION_COHERENCE);
-                    num_invalidates_++;
-                    coherence_entry->sharers[i] = false;
-                }
+            auto it = coherence_entry->sharers.begin();
+            while (it != coherence_entry->sharers.end()) {
+                int i = *it++;
+                if (i == id)
+                    continue;
+                caches_[i]->invalidate(tag, INVALIDATION_COHERENCE);
+                num_invalidates_++;
+                coherence_entry->sharers.erase(i);
             }
         }
     }
-    coherence_entry->sharers[id] = true;
+    coherence_entry->sharers.insert(id);
 }
 
 /* This function is called whenever a coherent cache evicts a line. */
@@ -120,20 +117,23 @@ snoop_filter_t::snoop_eviction(addr_t tag, int id)
     coherence_table_entry_t *coherence_entry = &coherence_table_[tag];
 
     // Check if sharer list is initialized.
-    assert(coherence_entry->sharers.size() == (uint64_t)num_snooped_caches_);
+    assert(!coherence_entry->sharers.empty());
     // Check that cache id is valid.
     assert(id >= 0 && id < num_snooped_caches_);
     // Check that tag is valid.
     assert(tag != TAG_INVALID);
     // Check that we currently have this cache marked as a sharer.
-    assert(coherence_entry->sharers[id]);
+    assert(coherence_entry->sharers.find(id) != coherence_entry->sharers.end());
 
     if (coherence_entry->dirty) {
         num_writebacks_++;
         coherence_entry->dirty = false;
     }
 
-    coherence_entry->sharers[id] = false;
+    coherence_entry->sharers.erase(id);
+    if (coherence_entry->sharers.empty()) {
+        coherence_table_.erase(tag);
+    }
 }
 
 void
diff --git a/clients/drcachesim/simulator/snoop_filter.h b/clients/drcachesim/simulator/snoop_filter.h
index c4f6c63d069..709b4d891ad 100644
--- a/clients/drcachesim/simulator/snoop_filter.h
+++ b/clients/drcachesim/simulator/snoop_filter.h
@@ -36,6 +36,7 @@
 #include <stdint.h>
 
 #include <unordered_map>
+#include <unordered_set>
 #include <vector>
 
 #include "cache.h"
@@ -45,8 +46,8 @@ namespace dynamorio {
 namespace drmemtrace {
 
 struct coherence_table_entry_t {
-    std::vector<bool> sharers;
-    bool dirty;
+    std::unordered_set<int> sharers; // IDs of caches sharing this line.
+    bool dirty = false;
 };
 
 class snoop_filter_t {