Howard Miller

As usual, I feel like I may not be asking a sensible question, but here goes anyway. 

I have a cache that I use to store some intermediate calculations. There is a keyed entry per calculation (storing a data object), and there are will be order or hundreds in each course.  If the basic data changes, I need to invalidate the cache. However, I only want to invalidate the cache entries for that course. I'm struggling to see anything in delete() or purge() that helps me with this. I can obviously prefix the keys with (say) the course ID but I can't see how that helps (no wildcard delete that I can see).

Can anybody steer me in the right direction / tell me how I'm thinking about this completely the wrong way?