public long getGCVersion(T mbr) {
    if (mbr == null || mbr.equals(myId)) {
      return localGCVersion.get();
    } else {
      synchronized (memberToGCVersion) {
        Long holder = memberToGCVersion.get(mbr);
        if (holder != null) {
          return holder;
        }
        return -1;
      }
    }
  }
returns the highest region-version of any tombstone owned by the given member that was reaped
in this vector's region
geode-core/src/main/java/org/apache/geode/internal/cache/versions/RegionVersionVector.java