private void _mapClear() {
    Executor executor = null;
    InternalCache cache = owner.getCache();
    if (cache != null) {
      DistributionManager manager = cache.getDistributionManager();
      if (manager != null) {
        executor = manager.getExecutors().getWaitingThreadPool();
      }
    }
    getCustomEntryConcurrentHashMap().clearWithExecutor(executor);
  }
Tells this map what region owns it.
geode-core/src/main/java/org/apache/geode/internal/cache/AbstractRegionMap.java