and the "self-documenting" way is to right click the origin of the rules and pick "reset"...
personally, i wonder if scribus really needs to move the origin of the rulers...
it can for sure be handy in some cases, but nowadays i think there are better ways to achieve the same result.
and the only time i hear of it is when somebody is stuck with the origin at the wrong place.
i think i've used it once many years ago. but nowadays i go for snapping items and setting the position manually (with calculations in the input fields).
or use the multiple duplication. (and then set guides?)
it does not even snap to items... (it only "snaps" to the margins and the page borders...)
does anybody have a good use case, that cannot be done more easily with other tools?
(if possible, a use case that is not a typical vector drawing task that is way easier to be done in inkscape)