When things get hot here in the mid-South, I do several things for my girls:
* Leave heavy casserole dish filled with ice in the yard. Girls can't knock it over, and as it melts they have nice cold water to drink. One of them also likes to walk on the ice before it melts.
* When there is no rain in forecast, I leave a big outdoor fan running at an angle to the run, so they can stand near it or not, as they prefer.
* Have plenty of shade. We put a tarp over the covered run and coop to cut down on rays.
* Exhaust fan inside coop that sucks air to outside. Reduces temp by a few degrees.
* Use old gallon jugs and fruit juice jugs as ice packs ~ we keep a bunch of these in a big freezer in the garage, and I put two jugs in the coop and one or two in the run each day. the girls like to sit on the flatter jugs.
* Electrolytes in water.
* Refrigerated melon slices, grapes, etc. as afternoon snacks.
According to the Gail Damerow Chicken health Handbook death can occur in poultry when temps reach 104 F, although I am hearing from a couple of folks in the southwest who have chickens tolerating 112.
Good luck!