No tick labels and adding title to groupplot generated plots

No tick labels and adding title to groupplot generated plots

I am generating an array of plots using pgfplots and more specifically the
groupplot environment. Here is an example:
\begin{tikzpicture}
\begin{groupplot}[group style={group size=2 by 2,horizontal
sep=0.2cm,vertical sep=0.2cm},height=3cm,width=3cm]
\nextgroupplot \addplot coordinates {(0,2) (1,1) (2,1)};
\nextgroupplot \addplot coordinates {(0,2) (1,1) (1,0)};
\nextgroupplot \addplot coordinates {(0,0) (1,1) (2,2)};
\nextgroupplot \addplot coordinates {(0,2) (1,1) (2,0)};
\end{groupplot}
\end{tikzpicture}
I would like to be able to eliminate either the x or the y tick labels or
both. I also want to add a different title to each plot. I have not found
a way to do this in the documentation. Any ideas?