There is nothing to do to clean the cache folder as it's all handled by rclone.
The common mistakes people make is that putting it to say 10GB and they have 50GB of files in use and are confused why it's not 10GB. There is no magic in terms of making space as the size would clean down to the max size with the exception of what files are in use.
If you have a 100GB file and a max cache size of 10GB, the cache area will be 100GB.