When you would like to clean that coffee grinder, simply add about a tablespoon of white rice and grind it. The oil and coffee residue will be picked up by the rice. Dump it and if you have a small brush (like a lady’s blush brush) use it to “sweep” the inside.
Rice will also clean your grinder of any spices that you have ground. The aromatic scent is absorbed by the rice and the grinder is left completely clean and ready to grind a different spice. You may also wish to use the “blush brush” as above for that final “sweep out”.