plone/plone.app.discussion — comment on commit 07b8ebc5df6d60f6b561771143304099beb6df4e
File:  line 0
By davisagli:

I think that rather than changing the modification time of the parent item, the correct thing to do would be make sure that when plone.app.caching calculates what URLs to purge for the discussion item, that list of URLs should include the parent item's main view. This can be done with an IPurgePaths adapter. plone.app.caching actually includes one for CMF discussion items (plone.app.caching.purge.DiscussionItemPurgePaths); presumably we need to add something similar for p.a.d comments.

As an architect of both plone.app.caching and plone.app.discussion, @optilude may be able to confirm this. :)