Hey thanks for this awesome plugin!

Until now I've always used handrolled scripts to setup caching in my jobs. Being able to declare caches with this plugin is just so much better! 

Most of my jobs are multibranch pipelines and I noticed that the cache would not be shared across my branches. My guess is that the caches are stored inside the workspace? Would it be possible to extend this plugin to allow storing caches in a arbitrary location on the master? That would allow me to re-use caches across branches.