The Astros did not comment.
Dominguez, 24, played in 152 games last season and hit .241 with 21 homers and 77 RBIs while playing top-notch defense at third base. Dominguez will be eligible for arbitration for the first time in 2016, while Grossman wouldn't be arbitration-eligible until 2017.
"Houston's my home and I love being an Astro," said Grossman, who grew up in the Houston area. "I want to be here as long as possible."
Like Grossman, Dominguez didn't want to comment on any potential contract talks.
"I like the city of Houston and I like playing here," he said. "If it happens, it happens. If they were to come to me and do that, I don't know. I'm just taking it day by day."
Astros general manager Jeff Luhnow has said repeatedly he'd like to sign Castro to a contract extension at some point. Last year, the Astros signed Jose Altuve to a budget-friendly four-year deal, and FOX Sports reported Wednesday they had offered prospect George Springer a seven-year, $23-million deal, which he turned down.
Brian McTaggart is a reporter for MLB.com and writes an MLBlog, Tag's Lines. Follow @brianmctaggart on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.