def clear_cache(backend=None):
    '''
    .. versionadded:: 2015.5.0

    Clear the fileserver cache from VCS fileserver backends (:mod:`git
    <salt.fileserver.gitfs>`, :mod:`hg <salt.fileserver.hgfs>`, :mod:`svn
    <salt.fileserver.svnfs>`). Executing this runner with no arguments will
    clear the cache for all enabled VCS fileserver backends, but this
    can be narrowed using the ``backend`` argument.

    backend
        Only clear the update lock for the specified backend(s). If all passed
        backends start with a minus sign (``-``), then these backends will be
        excluded from the enabled backends. However, if there is a mix of
        backends with and without a minus sign (ex: ``backend=-roots,git``)
        then the ones starting with a minus sign will be disregarded.

    CLI Example:

    .. code-block:: bash

        salt-run fileserver.clear_cache
        salt-run fileserver.clear_cache backend=git,hg
        salt-run fileserver.clear_cache hg
        salt-run fileserver.clear_cache -roots
    '''
    fileserver = salt.fileserver.Fileserver(__opts__)
    cleared, errors = fileserver.clear_cache(back=backend)
    ret = {}
    if cleared:
        ret['cleared'] = cleared
    if errors:
        ret['errors'] = errors
    if not ret:
        return 'No cache was cleared'
    return ret