An iframe can cause its parent window to scroll to another position, for example using document.body.scrollIntoView();

There seems to be no way to override (prohibit) this behaviour under the present w3c specification. StackOverflow user Kaiido has suggested a solution that exploits a bug in Chrome, which raises the question as to whether a CSS solution to prevent cross-source scrolling would be possible.

Further details at the StackOverflow answer.