def METHOD_NAME(self):
    """
    Finalize MapBuilder operations including removing orphaned documents
    """
    if self.delete_orphans:
        source_keyvals = set(self.source.distinct(self.source.key))
        target_keyvals = set(self.target.distinct(self.target.key))
        to_delete = list(target_keyvals - source_keyvals)
        if len(to_delete):
            self.logger.info(f"Finalize: Deleting {len(to_delete)} orphans.")
        self.target.remove_docs({self.target.key: {"$in": to_delete}})
    super().METHOD_NAME()