void prepareForClose(DiskRegion dr) {
    if (dr.isBackup()) {
      // Need to flush any async ops done on dr.
      // The easiest way to do this is to flush the entire async queue.
      forceFlush();
    }
  }
Called before LocalRegion clears the contents of its entries map
geode-core/src/main/java/org/apache/geode/internal/cache/DiskStoreImpl.java