By default you can "CTRL + LMB" on the "Brain" icon and it will reset all simulations. But I can't find a way to achieve this result via keyboard hotkey. The keyboard hotkey would be much more convenient than aiming every time on the Brain icon.
There is the "Reset simulations" action in the Hotkey Manager but it doesn't do the same as "CTRL + LMB on the Brain icon". (by the way I wasn't be able to find out what this action is doing really)