Make sure to have shade at all times. Also, keep their water cool and plenty of it. Larger water containers stay cooler for a longer period of time. Have the floor of the coop and run be sand and get a mister. The mister will cool it down dramatically and the sand absorbs the moisture and stays very cool. This makes a HUGE difference.
Once I got it all set up here in the Phx Valley, they stopped panting completely in the middle of the day and I noticed a big difference in their energy and activity. Before I made the change they were panting and laying around in the dirt having a difficult time. And one thermometer just down the street read 119 today (although everything else said only 115).
I turn my mister on at 11am on very hot days and turn it off at about 5pm. If it stays under 98 degrees, I try to leave it off for a day or so, rake the sand and let it dry out a little. This just keeps things from staying too we too much. But if it is staying in the hundreds, turn that mister on at or just before lunch until around 5pm or so. You'll notice a huge difference.
Also, depending on the size of your coop, you may need to adjust the number of misters that are working, depending on the type of mister you buy. I got one at Home Depot that has 5 nozzles. It was getting too wet so I plugged 3 of them and only 2 spray. It is perfect for my run area. So make sure you play with them until you find just the right amount...if you go this route.
Good luck! Your chickens can be happy in the heat if you do it right.....