Here in Western WA temperatures in the triple digits are unheard of, and we're pushing a week long heat wave. Today it hit 106.  I was cold hosing legs and bellies by noon. Fi did not even want to leave the water trough!  All the horses prefer the filtered water in
the shaded trough to bucket water, but Fi stood by it!  To keep them hydrated, all the horses are getting electrolytes in their water.  Normally we would do turnout at night and keep horses in the barn during the day, but the barn we inherited at this property is poorly ventilated and we now know that we have not properly fixed this issue for temperatures above 85 degrees.  So fans are blowing a cross breeze in the barn at night and horses go out during the day where they have shade and some breeze.  Last night I had to set up extra fans and a make-shift swamp cooler to cool down the barn before dark so we could bring horses in to feed.  The heat also brought the need for multiple stall and run in cleanings per day (keeps heat and flies down), extra fly spray,  and extra bucket cleanings (algea grows by the nanosecond in this hot sun).  When the heat started, I was riding early morning and late evening only, but I've taken the last 3 days off since my work schedule gives me only midday time right now.  It's just not worth a heat stroke.  We've been able to keep the horses healthy, hydrated and comfortable so far.
Hope you and your horse are cool!