The whole build agent root directory is managed as a docker volume, and retrieved from previous build, so you can easily benefit such caching if you configure maven to use adequate path for local repository (which should be the case by default, as /home/jenkins is slave root).
We also considered to offer an option to cache some path, comparable to travis-ci approach (based on tar.gz), so typically let end-user configure maven local repository as "cached". Backed could rely on additional volumes for this purpose, but definitively not on bind-mounts :P. This would let us investigate scalability challenge to distribute such a cache, maybe just by relying on docker volume-plugin features (but then relying on proprietary API), or maybe by using jenkins as a volume replication facility, à la TravisCI.