When we start using the "formatter URL" statements on properties to generate HTML links to authority vocabularies, we need a way to purge such cached renderings when the respective statement in the property definition changes.
As an interim workaround, I've put together a quick-and-dirty script to slowly do a rolling purge of items using pywikibot. It identifies all items that have not been edited since before the formatter URL was changed, generates a list, and works through them. As it uses the PWB framework it respects maxlag, and will back off if overloaded.
Works fine for small sets of items, but maxlag-related delays mean it's probably not a practical solution for very heavily used properties.