Store Docker buildcache to a separate file that can be reapplied after docker pull.
go get github.com/tonistiigi/buildcache/cmd/buildcache
After building your image run.
buildcache save -o cache.tgz imagename
This will create a small file cache.tgz that contains all known build cache for the image.
When you want to restore it in another machine run:
docker pull imagename
docker load -i cache.tgz
Build cache can only be applied if the pulled image is the same that was built. Easy way to check that is to check if the ID of the image that was first built is the same that you got after docker pull in another machine.
If docker load succeeds but cache still isn't being used in another machine try running docker history id-of-pulled-image and docker history id-of-built-image and compare the results to see where you got a cache miss.
Buildcache works with Docker v1.12 using only the remote API. To use buildcache in Docker v1.11 it needs to access the Docker storage directory directly. Use -g options to specify directory other than /var/lib/docker. Eariler Docker versions are not supported.
Note: Docker 1.13 added support for --cache-from flag to the build command, replacing the need for this tool.