Can a Nexus 6P be factory reset when screen cannot be used and phone off? I broke my Nexus 6P screen, so am replacing it - usually I would factory the phone. However, I can't as the screen is completely black. 

I power cycled the phone, but I am unable to enter the pattern to unlock the phone (fingerprint scanner only works after you enter the pattern after restart). 

I used Android Device Manager to wipe it, but as I can't decrypt it through entering my pattern, it isn't online, so can't be wiped.

However, does any of this matter if the pattern can't be entered after power cycling? Surely the device is encrypted so my data is secure. And if anyone manages to guess my pattern, the device will be online and ADB will wipe it.

Should I do anything else?
If you enter the password wrong too many times on your nexus device, it will factory reset your data (by default). It is also possible to factory reset through recovery mode by turning phone off, holding power and down volume simultaneously, clicking volume buttons until hitting recovery mode, then clicking factory reset.