Not sure if I am using the right terms in the subject line, but here is my problem:

I was in sheet view. I zoomed in to view a detail, such that the borders of my viewport went off-screen. I then decided I needed to make a small change in the model, so I just double-clicked to enter model space within the viewport. But now I can't figure out how to get out. Zooming and panning just happen in model space, so I can't get back to a situation where an area outside of the viewport is available for double-clicking to get out of model space.

Is there a command that gets me back to the sheet or viewport boundries, or takes me out of model space?