LoadedRound is straight up about cleaning cases BEFORE they go through your dies, especially for brass that has been on the ground. A vibratory cleaner will get the grit, sometimes a chemical cleaner is useful for ugly brass. If you think it is necessary, Universal decapping dies will remove the spent primer without resizing the case, then drop the deprimed brass into the crushed walnut hull cleaning media, turn it on and come back when it's clean.
Because I shoot mostly lead bullets, well lubricated, I do clean my dies occasionally. I use naphtha, sold at the grocery store as Ronsonol Lighter Fluid ($$$)and in the hardware store paint department as paint solvent ($$). Read the label, follow the precautions and remember that this is HIGHLY FLAMMABLE AND THE FUMES ARE DANGEROUS TO YOUR HEALTH! I disassemble the dies, removing obvious crud with a toothpick or shop rag, then gently introduce the die parts into enough solvent (held in a container that can be tightly sealed) to completely cover the parts. Let them soak for 10 or 15 minutes, then remove parts, cork the leftover solvent, lightly oil (Kroil) and re-assemble. This cleaning process should be done in an area that is well ventilated and safely away from any chance of a spark. The dies should be clean, lightly lubricated and wiped down, then adjusted to a dummy round. If you are shooting only jacketed bullets, cleaning of dies is rarely needed.
Dirty brass can scratch expensive dies. I do not reload brass without cleaning it first. I am also sold on the value of the hardened (carbide or nitride) sizing dies, which leave the brass with a polished look. Try cleaning your brass first and see if you have better results.
Border Hopper