Remote Triggered Switch for a Water Heater socket
You are describing a 3-way switch, which is among the most cheap and common electrical elements you will find.

You can pay up a bit for a 3-way switch with "pilot light" which will illuminate the switch when the circuit is closed (or open, depending on how wired), so that users will know whether toggling the switch will be turning the receptacle on or off.

Given the purpose you describe I would actually run the receptacle off of two single-pole switches wired in parallel so that it is on if either bathroom is calling for heat.

And yes, there are plenty of wireless solutions to toggle power at a wall receptacle if you want to spend the money for them instead of hard-wiring a 3-way switch.