'Remove the cached reference.'

@classmethod
def _flush_cached_by_key(cls, key, force=True):

    try:
        if (force or cls.at_idmapper_flush()):
            del cls.__dbclass__.__instance_cache__[key]
        else:
            cls._dbclass__.__instance_cache__[key].refresh_from_db()
    except KeyError:
        pass
