    # File lib/chef/cookbook_version.rb, line 406
        def self.cleanup_file_cache
          unless Chef::Config[:solo]
            # Delete each file in the cache that we didn't encounter in the
            # manifest.
            cache.find(File.join(%w{cookbooks ** *})).each do |cache_filename|
              unless valid_cache_entries[cache_filename]
                Chef::Log.info("Removing #{cache_filename} from the cache; it is no longer needed by chef-client.")
                cache.delete(cache_filename)
              end
            end
          end
        end