prerender: 304 status response

I’m use Phantomjs 2, prerender-node middleware and own prerender service. On first request on http://mysite.com/?_escaped_fragment_= I’m got my prerendered page. It’s ok. But in second times I’m got empty body and 304 status. The same thing when i try in other brouser, where this page wasn’t open before. In anonymizer the same problem. Empty page and 304 status. It’s looks like Phantome keeps rendered page in cache. But i don’t know, how to clear it. Or this is how it should work?