No... actually you need for EACH UNIT in the aoe MATCHING CONDITION to create a dummy unit and order the dummy unit to cast doom at (Picked Unit). Don't forget to add the Expiration Timer.
Why this? Because a single unit cannot cast simulatenous on more than one unit the ability. Every ability has a casting time (around 0.50 or something) in which it is focusing to cast the ability and cannot be interrupted. Some take even more, abilities such as Chain Lightning.
Actually not... Just use a "Pick Up Every Unit" and do actions -> Create 1 dummy at position of (Picked Unit) -> Order (Last Created unit) to Doom (Picked Unit) -> Add 1 seconds Expiration Timer to (last created Unit)
Well when I said how to do it I assumed he would know to put an expiration timer and all the conditions. And you are wrong about the casting time, you can change their cast time to 0, by changing "animation cast backswing" or whatever to 0