Pipeline docker cache key

[Ben van Klinken]

If I have two steps which need to cache docker images, how can I use different cache keys for each step?

 steps:
   - step: 
      caches:
       - docker
     script:
       - do something
   - step: 
     caches:
      - docker
     script:
      - do something else

how can i get the two steps above to use different cache keys? currently only one of them gets cached correctly