Well, I am fascinated!
164 posts so far, much discussion about MEGA 2560s and other matters, and you do not appear to understand how a microcontroller works. :astonished:
An output "port" is in fact a latch, based on a flip-flop which maintains the state to which it is written by the corresponding "write" instruction. It will generally be cleared - set to zero - by the reset process of the microcontroller and in many or most microcontrollers, the port may be defined to be either an input or an output.
This is in contrast to the general notion of a microprocessor which offers not a latch, but a data bus, address and control signals which can transiently execute commands to send data to external hardware with the intention of that particular external hardware latching the data and acting on it.
Communication between different processors is a quite complex matter, generally executed by some protocol such as asynchronous serial transfer (using a UART) or a clocked serial protocol (thus requiring two lines) such as I2C or USB.
So it is generally a very inefficient way of sharing processing tasks (unless special hardware is built into the processors) because such communication becomes as complex and time-intensive as the other tasks themselves which are intended to be so delegated.