I think you're thinking about the tax-free sale of a personal residence. In the USA, you are taxed on gains in excess of $250,000 ($500,000 if Married Filing Jointly), provided house was lived in AND owned for at least two out of the past five years. You clearly do not currently live in the property, so the live-in rule has an effect on your sale.
If you lived in it for less than two out of the past five years, you are allowed a prorata reduction of the $250,000 gain exclusion provided the move was for an extenuating circumstance. The fact that you are working on an overseas work assignment would count as an extenuating circumstance. The prorata reduction is up to the five year mark.
No more purchasing of another property required.
There is a different exception you may be thinking about, the tax-free exchange of one business property for another, called a Like-Kind exchange or a 1031 exchange. You cannot exchange a US property for a non-US property, so this will not work for you.