Nginx proxy cache

I am using Nginx to proxy the backend server and I need to know if Nginx will disable its proxy cache as described in the http standard.
I also need to know how Nginx interprets the Cache-Control: must-revalidate response header from the proxy server.

Specifically the questions are as follows:

1. If I send a request to a specific resource by PUT method, does this mean that Nginx should clear its cache for all methods of requesting this resource so that the next request to this resource (for example, the HEAD method) writes to the cache the already updated response for such a request to this resource.
2. If I send a request to a specific resource by the GET method and my backend server responds to a request with this method with a response containing the Cache-Control: no-store, must-revalidate header, does this mean that Nginx must clear its cache for all methods of requesting this resource so that the next request to this resource (for example, by the HEAD method) writes an already updated response to the cache for such a request to this resource.

In the Nginx documentation, I didn't find anything about cache invalidation regarding the standards.

If anything:
My backend server does not generate ETag,
I know that in Nginx caching of responses from the proxied server is disabled by default.