Tracking Cohort Usage and Last Access for Efficient Cleanup

Is there any way to tell where a cohort is being used (eg in other cohort definitions, or in which reports), and when it was last used - similar to how the Lexicon shows query count and last query date for events? We've got a heap of cohorts and would love to be able to clean them up, but it's very scary to risk deleting a cohort and breaking an unknown number of reports with an unknown impact etc.