Nested grep

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When grepping for something I often follow a certain match and do
another grep to find out more about it. The problem is this eliminates
the original grep buffer (with matches, current state, etc.), so I have
to redo that grep (and start from the first match again if I use
next-error) to continue investigating other matches.

I'd like a nested grep feature for starting an other grep with the
ability to return easily to the previous grep results after I'm
finished with the current one.

Is there an existing package which does something like that?