public long lockForClear(String regionPath, DistributionManager dm,
      InternalDistributedMember locker) {
    lockVersionGeneration(regionPath, dm, locker);
    return localVersion.get();
  }
locks against new version generation and returns the current region version number
geode-core/src/main/java/org/apache/geode/internal/cache/versions/RegionVersionVector.java