Munster head coach Foley was found dead in his hotel room on the eve of the Irish province's European Champions Cup match with Racing 92.
The former Ireland backrow forward, capped 62 times, died in his sleep at the age of 42 and left a widow, Olive, and two young sons.
Munster captain O'Mahony was close to Foley and he said that returning to Paris had revived memories of that terrible time.
"Look, it was funny, myself and Johnny (Sexton) had a conversation about it on the way to the South Africa game," he said at the Irish press conference ahead of the Scotland game.
"Sometimes it's weird to be in Paris and think about 'Axel' and what happened.
"It's an incredibly sad memory for the Munster team who were in Paris that week.
"'Axel' is always someone who's in my head on a very regular basis.
"When you come to Paris, what certainly comes to mind are the fondest memories we had together and the amount of inspiration that he gave not just to me but lots of young kids in Munster and Ireland."
O'Mahony, 34, is more phlegmatic about becoming the 10th Irish player to reach the 100-cap mark - a list that includes fellow Munster legends Ronan O'Gara, Keith Earls, Conor Murray and John Hayes.
"I'm just trying to prepare as if it's another Test match," said O'Mahony.
"Hopefully I can get all this stuff out of the way as early as possible.
"Maybe when I'm sitting on my own with a coffee I might have a quick think about it, but I'm hoping there’s going to be bigger moments in my career than this one - and hopefully in the near future."
Ireland will qualify for the World Cup quarter-finals with a win or a draw against the Scots at the Stade de France.
