Even better than DotA's system, have a periodic trigger select every hero on the map set mana to 100% and refresh all cooldowns.
Unit - A unit Begins casting an ability
((Casting unit) is A Hero) Equal to True
Unit - Set mana of (Casting unit) to 100.00%
Unit - Reset ability cooldowns for (Casting unit)
[B]Unit - A unit Starts the effect of an Ability[/B]