Went to https://example.com, checked that it's cached in the inspector, clicked on the More information link which leads to https://www.iana.org/domains/example, unplugged my connection (went offline), clicked back. It showed the cached https://example.com. I clicked forward. It showed the cached https://www.iana.org/domains/example page. Clicked back/forward like a maniac, the pages switched seamlessly.
Repeated the same process on a non-cacheable page, it showed a dud when disconnected as expected.
Tested on Firefox and Chromium.