The requirement is that you permanently RESIDE in the United States. Even if you vacation somewhere abroad, you are still residing in the United States. An American astronaut who spends 3 months aboard a space station still resides in the United States.
Only once you have been gone for 6 months, or you have been leaving the United States frequently, will CBP upon your arrival ask you to prove that you have not abandoned your US residency. This rule is basically in place, to avoid people who have Green Cards to live outside the US and then just "visit" the US once in a while to pretend they are residing in the US.
An immigrant from Europe, I live on the American Riviera and work as an attorney in Santa Barbara, California.