How to clear the cache of nginx?

I had the exact same problem - I was running my nginx in Virtualbox. I did not have caching turned on. But looks like sendfile was set to on in nginx.conf and that was causing the problem. @kolbyjack mentioned it above in the comments.

When I turned off sendfile - it worked fine.

This is because:

Sendfile is used to ‘copy data between one file descriptor and another‘ and apparently has some real trouble when run in a virtual machine environment, or at least when run through Virtualbox. Turning this config off in nginx causes the static file to be served via a different method and your changes will be reflected immediately and without question

It is related to this bug: https://www.virtualbox.org/ticket/12597

You can also bypass/re-cache on a file by file basis using

proxy_cache_bypass $http_secret_header;

and as a bonus you can return this header to see if you got it from the cache (will return 'HIT') or from the content server (will return 'BYPASS').

add_header X-Cache-Status $upstream_cache_status;

to expire/refresh the cached file, use curl or any rest client to make a request to the cached page.

curl http://abcdomain.com/mypage.html -s -I -H "secret-header:true"

this will return a fresh copy of the item and it will also replace what's in cache.