The purge remote media API allows server admins to purge old cached remote media.
The API is:
POST /_synapse/admin/v1/purge_media_cache?before_ts=<unix_timestamp_in_ms>
{}
... which will remove all cached media that was last accessed before
<unix_timestamp_in_ms>.
To use it, you will need to authenticate by providing an access_token for a
server admin: see README.rst.
If the user re-requests purged remote media, synapse will re-request the media from the originating server.