Question: purging a package from the store

[Pjotr Prins]

Our caching server gives a consistent failure for one package. It
exists in the store and 'guix gc checks' pass.

  guix substitute: error: download from
  
'http://guix.genenetwork.org:8080/nar/sqd3q1xq5fsbga00bwhghi9shi7xdaac-gtk+-3.18.2'
  failed: 404, "Not Found"

Now I want to purge it without running a full gc. Next reinstall it
and see if it gets fixed.

What is the suggested method for fully purging a package from the store?

Pj.