The windows 10 minecraft client doesn't appear to implement any cache management of the folders CatalogCache or CatalogScratch under

%user%\appdata\local\packages\Microsoft.MinecraftUWP_8wekyb3d8bbwe\LocalCache\minecraftpe\

and there's no "Purge marketplace cache" or anything in the windows 10 minecraft client under storage management. it's just unmanagable and not automatically curated or managed by the client. near as i can tell it just builds endlessly with browsing the market place.