Creating a viewport in modelspace?

Dear Reader,
I need some help using Autocad. I'm currently working on a drawing that has multiple views of one floor; construction view, mechanical view, electrical view, and so on...
I got these views and used XREF to place them next to eachother. So now I have a drawing showing the same floor (e.g. 1st floor) three times.
What I want to do is create some kind of viewport wich I can project over all three XREFS, so that if I make a change in one place of my drawing it automaticly updates the other two versions.
For example, if I make a change in the construction part of my drawing and then after that zoom in to the mechenical part, the changes I've made will show there as well...
I want to do this in modelspace.
Can anyone help?
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