The East Junction layover facility is an MBTA creation. When Conrail gave up the operation of the Boston Commuter operation and the Boston and Maine was chosen to operate it, March, 1977, service between Boston and Providence was operated out of Providence. There were some Attleboro turns but no equipment was stored there. Subsequently, there was a funding impasse and the MBTA quit running to Rhode Island for a number of years. The East Junction layover dates from sometime in the 1980s. I couldn't give you a more precise date.
At one time there was a freight yard in the same area and served several local industries. I think Thompson Chemical was a major one.