Dirtycat is a medium size 5yr old neutered boy. We've had him for almost a year. Lately another cat (also medium sized) has been coming in the garden, sometimes right up to the house and down the side return. They haven't fought or anything (to my knowledge) but they've had a few face offs: a week ago I found dcat sitting in top of our fence meowing and staring at strangecat in ndn's garden. I left them to it as I think dcat has a right to defend his territory. Today though strangecat was sitting in top of ndn's shed and staring down at dcat. Again I left them to it but then a few minutes later dcat came trotting to the house looking unhappy 
. I went out and chased it off and gave dcat tummy rubs on the sofa to cheer him up. Am I being ridiculous to worry about this? I feel like dcat is getting bullied in his own garden and he's been spending more time in doors (cat flap has a microchip lock) - granted this has also coincided with the cold weather. Is there anything I can do, anyway? Should I chase strangecat off myself even when dcat is trying to deal with it himself?
Someone please tell me to get a grip..