"Zapping" a cache means forcing the Retrieval Cache Period and Missed Retrieval Cache Period to time out. To "zap" a cache, you can use the Zap Cache REST API, or the platform UI.
To zap a cache using the platform UI:
In the Artifacts module tree browser, select the repository cache you wish to "zap".
Click Zap caches in the right-click menu or from the Actions drop-down menu.