Caching problems

Hi,

Our wordpress theme loads some additional content from external sources, for instance RSS feeds, data from web services, data from a vBulletin forum and so on. This additional content is displayed on the front page, together with the latest WordPress posts. We’ve had this feature for more than one year without any problems (WordPress versions 3.6 up to 4.0).

After upgrading to WordPress 4.1, some users started to complain that quite often the additional content on the front page is updated, but they still see the old content until they hit Ctrl+F5, bypassing the caches.
We don’t do any magic with the additional content. Some parts of it are buffered in the database, but usually the content is displayed without any special caching.
As far as I know WordPress has some logic to decide when it should set the nocache HTTP header and of course this logic cannot know about the additional content that we load.

So my question is: Assuming I want to display dynamic external content on the WordPress start page, how can I make sure WordPress gets informed about changes in this content? I don’t want to disable caching completely.

Regards
TiKu