You should seek Luxembourg advice on whether you have a tax liability there.
You will be subject to Irish CGT on the sale of a property here. The element of the gain relating to when it was your principal private residence (and the last 12 months of ownership are deemed to have been your PPR) will be exempt from tax. The exempt element is calculated on a time basis.
Your gain will be in the region of €164,000 (315k - (124.4 k * 1.21) and take away other costs of acquistion and sale)). You have owned the house for 9 years. Of that, let's say it was your PPR for 3 years. It is deemed to be your PPR for the last year too, so that gives us 4/9 years exempt, or 5/9 years of gain taxable. This leave you with €91,000 taxable at 20%, or a tax liability of €18,222.
You should note that it will be deemed to be your PPR for all the time of ownership if your absence from it was when you were working abroad (which I take it you are) and you live in it both before and after that time abroad. So, if you were to come home for a short while and live there, you may be able to sell it without any liability to Irish tax.