FYI, the SU2 release notes has this line item:
- Added option to reduce rolling cache size inside the game, at the cost of clearing current cache.
So, whilst not a specific option under Rolling Cache Settings, nor a perfect solution for your wish, one can now clear the cache by reducing the cache size. I have not tried this, but I suspect that it may also require restarting the sim to take effect. One could then increase the cache size again if one wanted to.