Put a 1k resistor inline with the wire. If one pin goes output high and the other pin goes output low and both chips are run from 5 volts, without the resistor, the PICs will try to pass XX amount of current, possibly damaging the pin drivers. With the inline 1K resistor, the max current that could pass between the 2 PICs on said line would be limited to around 5mA....well within the PICs limitations.

Unless you have this line connected to the heating pad that is set up to burn somebody's skin...then you may want to run both PICs at 100VDC and let that unlimited thousand amps of current flow...