You will need to write a macro in the Change event of the first comboBox.
That macro will need to test the value of the box  and if it is "Global" set
the second ComboBox Value to "All"

You may also want to set the second ComboBox to Locked so the user cannot
change it without coming back to sheet  1 and changing the first ComboBox to
"regional".

Don't forget if you do this to unlock the second box if the first box is
changed to Regional