Domínguez won a silver medal with Spain at the 2018 FIBA U16 European Championship in Serbia, averaging 8.9 points. At the 2019 FIBA U16 European Championship in Italy, he was named most valuable player after averaging 13.4 points, 3.4 rebounds and 2.3 assists per game and leading Spain to a gold medal. Domínguez led his team to fifth place at the 2021 FIBA Under-19 World Cup in Latvia, averaging 18.7 points, 2.9 rebounds and 2.4 assists per game.