protected void onInvalidCacheEntry(RouterException routerException) {
      setChunkException(routerException);
      chunkCompleted = true;
      retainChunkExceptionOnSuccess = true;
      chunkIdIterator = null;
      dataChunks = null;
      numChunksTotal = 0;
      numChunksRetrieved.set(0);
    }
On an invalid cache entry, set a {@link RouterErrorCode} exception for first chunk, mark the chunk
as completed, and set the chunk counters such that the operation will be completed.
@param routerException Exception due to which cache entry was invalid.
ambry-router/src/main/java/com/github/ambry/router/GetBlobOperation.java