You can have the processor hardware reset itself with external hardware to hold the pulse. You can't do it without some form of pulse stretching because as soon as the outputs resets the chip it turns to an input and all bets are off.
A simple diode and cap may do the trick, I've not thought about it much. A uC supervisor chip would be better I think, many of them have an input for a push button, you could control that.
Rob