Invasion Rules

Hi everyone. If I have already defeated the boss in a zone, am I still able to be invaded? I usually am a Mound-Maker, but I wanted to use the Way of Blue covenant on to try and give the Blue Sentinels some love.

I have used dried fingers and am Embered. I know you cant summon others with white soap signs if you have killed the boss in a zone, but what about still being invaded if you are just walking around?