qubes-core-admin-linux/tools/qvm-xkill

#!/bin/sh

set -e

ID=$(xdotool selectwindow)

xprop -id "$ID" _QUBES_VMNAME | grep -q ' = ' \
  || { echo "${0##*/}: Not killing dom0 window $ID" >&2; exit 1; }

xdotool windowkill "$ID"