private static void closeCache() {
    if (cache != null && !cache.isClosed()) {
      cache.close();
      cache.getDistributedSystem().disconnect();
    }
  }
unregister a key for a particular client in the server

@param clientId the client's ID
@param key the key it's no longer interest in
geode-core/src/distributedTest/java/org/apache/geode/internal/cache/tier/sockets/InterestListDUnitTest.java