I frequently have one root project open which I've :cd'd to. I also have other tabs with :lcd's set. This is great and works really nicely, but occasionally I end up looking at something in the main project as a result of opening a Buffer from the main project in one of my other windows...

at this point I'd like to do something to swap out of :lcd mode and back into :cd mode.

Reading :h cd I can't work it out.

It states:

When a :cd command is used, the current window will lose his local current
directory and will use the global current directory from now on.

However as I'm running on linux just running a blank :cd actually wipes out my global directory and sets it to ~

I can't find a way of accessing the :cd value that isn't modified by having an :lcd set