Linux Libertine with Greek Small Caps


\documentclass{article}% lualatex or xelatex
\usepackage{fontspec}
\setmainfont[SmallCapsFont=LinLibertineOC,% fontname may be different
             SmallCapsFeatures={Letters=SmallCaps}]{Linux Libertine O}
\begin{document}
\textsc{Small Capitals}
\textsc{Πεζά κεφαλαία}
Πεζά κεφαλαία

\end{document}