klayout greyhound_ihp_top.gds.gz -s greyhound_ihp_top.gds.gz
display level 1
select upper half of the chip and delete the selection.
This only deletes references/geometry of the first layout, not the second one.
Repeating the select/delete sequence is needed to delete the references/geometry of the second layout.
"select by area" should select references/geometry in both layout's.