Any problems with caching big, complicated query results in a multi-tenant SaaS?

Hey everyone, I'm building a multi-tenant SaaS app, and some of my tenants run these seriously complex analytical reports. I mean, these queries dig into a huge amount of data and they can really take their sweet time. So we've been thinking about caching the results. But here's the thing. the queries are super custom, and each tenant's data is always changing. I'm kinda stressed about how we'd clear out the cache and, just as important, keep each tenant's data totally separate. Has anyone out there dealt with this kind of problem before? Any good ideas for getting rid of old cached stuff for specific tenants? Or, you know, any epic fails I should definately steer clear of?