@classmethod
def clear_instance_cache(cls):
    """
        Clear the cache of filesystem instances.

        Notes
        -----
        Unless overridden by setting the ``cachable`` class attribute to False,
        the filesystem class stores a reference to newly created instances. This
        prevents Python's normal rules around garbage collection from working,
        since the instances refcount will not drop to zero until
        ``clear_instance_cache`` is called.
        """
    cls._cache.clear()
