Flag stream change cache after persisting events with new stream order

This appears to have previously been done within the room depth handling
and only for local events.

synapse/storage/databases/main/events.py

@@ -487,6 +487,14 @@ def _persist_events_txn(
         # NB: This function invalidates all state related caches
         self._update_current_state_txn(txn, state_delta_for_room, min_stream_order)
 
+        # Flag the stream change cache for this room if we added non-backfilled events
+        if max_stream_order > 0:
+            for event, _ in events_and_contexts:
+                assert event.internal_metadata.stream_ordering is not None
+                self.store._events_stream_cache.entity_has_changed(
+                    event.room_id, event.internal_metadata.stream_ordering
+                )
+
     def _persist_event_auth_chain_txn(
         self,
         txn: LoggingTransaction,
@@ -1046,6 +1054,9 @@ async def update_current_state(
                 stream_id=stream_ordering,
             )
 
+            # Flag the stream change cache for this room
+            self.store._events_stream_cache.entity_has_changed(room_id, stream_ordering)
+
     def _update_current_state_txn(
         self,
         txn: LoggingTransaction,