default void postClearRegionBlockCache(ObserverContext<RegionServerCoprocessorEnvironment> ctx,
    CacheEvictionStats stats) throws IOException {
  }
Called after clearing the block caches for one or more regions
@param ctx   the coprocessor instance's environment
@param stats statistics about the cache evictions that happened
@throws IOException if you need to signal an IO error
hbase-server/src/main/java/org/apache/hadoop/hbase/coprocessor/RegionServerObserver.java