Is it strictly mulch or is other organic matter mixed in? It really doesn't "require" cleaning as long as the volume of litter is sufficient to allow the poop to compost in place, and yes for that you want some moisture to help the process along. You will likely find it beneficial to remove some of the material once in a while due to build up but that could be once every few years, depending (again, without knowing what volume you're working with I can't comment on frequency).
This is an example of my deep litter run for my flock, and clean out after roughly 3 years of accumulation:
https://www.backyardchickens.com/threads/prepping-deep-litter-for-fall.1599199/