@Override
  public boolean evictBlock(BlockCacheKey cacheKey) {
    LruCachedBlock cb = map.get(cacheKey);
    return cb != null && evictBlock(cb, false) > 0;
  }
Whether the cache contains block with specified cacheKey
@return true if contains the block
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/LruAdaptiveBlockCache.java