Ok guys...I heard this one today and do not agree with the answer: Two 3-ways control a house back porch light and two coach lights on a detached garage. The garage has a small sub-panel fed from the house. I was told only three ungrounded conductors were needed between the garage and house because the existing neutral for the back porch light is connected to the house service panel while the neutral for the garage coach lights are connected to the garage sub-panel. I say this is not correct because branch circuit neutrals have to be terminated at the origin of the branch circuit. If the branch circuit feeds from the garage sub-panel...then the neutral must also feed from the sub-panel. If the branch circuit feeds from the main house panel...likewise the neutral must also feed from the house panel since this is the origin of the branch circuit. Comments please !