We have a break from the heat here right now, but inquired to these good folks when I needed the same advice. Was told that chickens can only give off body heat through comb and waddle, legs and feet and also by holding their wings out to let blood vessel in that area give off body heat. I took a shady spot in my chix yard and placed shallow pans (used shallow red heavy duty plastic paint trays as they were cheap) that I fill with water. I also spray the ground around that area several times a day and change water in the trays. The chix gravitate to that spot, get in and out of the water and generally act silly.
I also have concrete block chix house and have discovered that when I keep the people door closed that the temps inside stay about 8 degrees cooler. When I feel it needs it I spray the roof and block walls with the hose as I spray the shady spot and change water.
People laugh at me with what I do for my babies, but you guys all understand. Good luck with the heat, Leslie