@VisibleForTesting
  public static void resetInstance() {
    ccnSingleton = null;
  }
Factory method to construct a CacheClientNotifier {@code CacheClientNotifier} instance.

@param cache The GemFire {@code InternalCache}
@param clientRegistrationEventQueueManager Manages temporary registration queues for clients
@return A {@code CacheClientNotifier} instance
geode-core/src/main/java/org/apache/geode/internal/cache/tier/sockets/CacheClientNotifier.java