Are you in the Northwest? We are in Western Washington and have had all time record temps, and we have been challenged by the heat, too. It was 104 on Wednesday! We are usually in the 70s or 80s, maybe low 90s, so this is all new to us. 
We set up a fan in our rafters to foster air flow. Also put out pans of water for them to stand in and drink from. Wet down the run so they have cool earth. I've heard of misters being used, some people even using the head old an adjustable spayer set on mist mounted above the pen. Chickens seem to not like getting wet (rain) so I'm not sure how that would work. Also, water melon, grapes, lettuce for a treat in the hot part of the day.
Don't laugh, but DH and I took turns with a spray bottle of warm water and misted them down on the 100 plus days. It DID help, we didn't lose a single bird. They were panting, wing spreading, lathargic, - it was pitiful! But they seemed more comforatable after the mist.
I know hot climate people think we are weenies (I used to live in Phoenix, I Know), but it's hard for man or beast to tollerate heat if they are not accustomed to it!