@Override
  public void stop(CoprocessorEnvironment env) throws IOException {
    RegionCoprocessorEnvironment renv = (RegionCoprocessorEnvironment) env;
    this.cache = null;
    ((ZKDataHolder) renv.getSharedData().get(ZKKEY)).release();
  }
Internal watcher that keep "data" up to date asynchronously.
hbase-examples/src/main/java/org/apache/hadoop/hbase/coprocessor/example/ZooKeeperScanPolicyObserver.java