The Big Bang involved the entire universe. At the beginning the Big Bang happened everywhere at once. The present location and velocities of galaxies are a result of a primordial blast known as the Big Bang. It was beginning of the Universe and the beginning of time.
Source: Cosmic Journeys - To the Edge of Gravity, Space and Time. Structure and Evolution of the Universe Roadmap 2003-2023http://universe.gsfc.nasa.gov/roadmap/roadmap99_lores.pdf [Date accessed 29 May 2000]