A way to check / clear the local DNS cache

Would be great to see what domains are cached in the app and have the ability to delete specific ones and or clear the lot to do a full refresh. 

Would also be great to have a better explanation of how caching works too. 

For example.. if I've set a custom DNS before enabling the cache DNS feature, does it then resolve all domains from the Customised DNS and then cache the results? 

I ask because the combo of EERO with Caching and nextdns would be perfect if that's the case.