Ulster dominated the first half but were unable to convert their superiority into points, going in 6-3 ahead at the break thanks to Ruan Pienaar's boot.
Paul Warwick kicked Munster back in contention before Dineen's break-away score, but McGahan was keen to underline the teamwork that went in to the victory.
"I thought he (Dineen) defended extremely well, he chased hard, carried strongly and got a just reward to give us a well deserved victory," said McGahan.
"But overall, we asked for a huge effort from the forwards and I believe we got it; right across the park the forwards were very good, from the set pieces to their work at the contact areas, both in attack and defence.
"We were missing 21 players, we were here in Ravenhill against a good Ulster side and not many sides come away from here with a result, not to mention denying them a bonus point."
Rhys Priestland kicked all of Scarlets' points as they overcame a spirited Glasgow fight back to win 18-14 at Parc Y Scarlets.
Despite leading 15-0 at one point, Lou Reed's sin-binning and tries from DTH van der Merwe and Duncan Weir, who also kicked both conversions, made it a nervy finish for the home side.
Cardiff Blues enjoyed total dominance over Aironi as they brushed aside the Italian side 20-3 in Italy, including 10 points from man of the match Ceri Sweeney.
Tries from Richard Mustoe and Lloyd Williams helped the Blues maintain their 100% record against Italian sides, with Ludovic Mercier kicking the Italians' three points.