# Passive form - The exact difference between を and が?

I've seen this question asked before, but i feel the answer didn't quite answer all my questions, so here goes. Now, I am rather sure that this: >ケーキが食べられた Means: >The cake was eaten. (by someone) Now, recently I've noticed a few cases where the passive form was used with "を" instead of "が". Judging from the examples I've seen, I would guess that: >ケーキを食べられた Means something along the lines of >*my* cake was eaten (by someone) However, can this be used with someone elses cake instead of my own? I guess what I'm basically asking is whether this is possible: >犬は猫にケーキを食べられた And if it is, does it mean: >*The dog's* cake was eaten by the cat Or can the Aを(passive verb) construction only be used when I'm speaking of something directly relating to myself, the speaker?