protected void markDepartedMember(T id) {
    synchronized (memberToVersion) {
      RegionVersionHolder<T> holder = memberToVersion.get(id);
      if (holder != null) {
        holder.isDepartedMember = true;
      }
    }
  }
This marks the given entry as departed, making it eligible to be removed during an operation
like DistributedRegion.synchronizeWith()
geode-core/src/main/java/org/apache/geode/internal/cache/versions/RegionVersionVector.java