Hi,
FYI, I suggested to the Nginx Helper plugin project to add a "purge all" option:
Add option to purge all pages (and make it default?) · Issue #246 · rtCamp/nginx-helper
In the meantime, I consider Nginx Cache plugin safer to use (as it clears the whole cache everytime), unless you are testing every use cases of your website and making sure that caching is correctly cleared when it should.
Interested to hear any thoughts 🙂