Drinking glasses, according to the Shulchan Aruch, may be used for drinking hot or cold drinks at meat and dairy meals interchangeably, as long as they are thoroughly cleaned between usages. Many Sephardic Jews follow this ruling.
According to some Poskim, even Ashkenazic Jews can rely on this Psak. (See Shu”t Mishneh Halachos Vol. 9 Siman 168 and Shu”t Teshuvos V’Hanhagos Vol. 1 Siman 432 who learn that the Rama was only stringent with glass for Pesach usage and not for meat and dairy during the year)
However, it is praiseworthy for everyone (even Sephardim) to be stringent and keep separate glasses for use with each food class. (Shu”t Teshuvos V’Hanhagos ibid. and Shu”t Tzitz Eliezer Vol. 8 Siman 20 and Vol. 9 Siman 26)