Can the viewport be scaled reset without a hard refresh?

In a mobile safari (for example), if a user is on a full site and then switches to mobile, he maintains the previous viewport zoom.

How do I force the browser to do a one-time forgetting of the remembered scale?

A Javascript solution would be better, but open to other ideas.

added:

Found this more correct question intended for android:

** How to reset the scaling of a viewport without refreshing the full page? **

But I also see the same issue on ios, without hard setting the page scale is never reset.