'Iterate over our local cache items, and
remove the keys that are beyond their grace time.'

def clean_local_cache(self):

    to_expire = []
    now = int(time())
    try:
        for (k, (_, _, grace)) in six.iteritems(self._local_cache):
            if (now > grace):
                to_expire.append(k)
    except RuntimeError:
        return
    for k in to_expire:
        try:
            del self._local_cache[k]
        except KeyError:
            pass
