The following extracts from JEDEC standards provide guidance:
Power pins that are directly connected by metal (inside the package) form a power pin group. A power pin is defined as any pin intended to provide power to any portion of the IC. Any pin that is intended to supply power to another circuit on the same chip must be treated as a power pin. However, if a pin is intended to supply power to a circuit on another chip but not to any circuit on the same chip, it may be treated as a signal pin. Any pin that is intended to be pumped above the positive supply or below the negative supply of its circuit block must be treated as a power pin (example: positive and negative terminal pins connected to a charge pump capacitor). Programming pins that do not draw current should be considered as I/O pins (example: Vpp pins on memory devices).