private long basicGetLastModifiedTime() {
    return lastModifiedTime.get();
  }
The logical lastModifiedTime of a region is the most recent lastModifiedTime of the region and
all its subregions. This implementation trades performance of stat retrieval for performance of
get/put, which is more critical.
geode-core/src/main/java/org/apache/geode/internal/cache/AbstractRegion.java