https://bugs.freedesktop.org/show_bug.cgi?id=64850
--- Comment #14 from Jakob Nixdorf flocke@shadowice.org --- 'xrandr --output DVI-0 --off' causes the first screen (HDMI-0) to turn black too, and the DVI screen gets really switched off (monitor switches to standby).
Blind-typing 'xrandr --output DVI-0 --auto' turns the DVI screen back on (still only a black screen) and the HDMI screen also stays black.