\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{pgfplots}
\pgfplotsset{compat=1.8}
\begin{document}
\begin{tikzpicture}
\begin{axis}[xmin=0,xmax=1,ymin=0,ymax=1,]
	\addplot+[domain=0:1] {x};
\end{axis}
\begin{axis}[xmin=0,xmax=1,ymin=0,ymax=1,,ytick pos=right]
	\addplot+[red,domain=0.6:0.8] {x};
\end{axis}
\end{tikzpicture}

\begin{tikzpicture}
\begin{axis}[xmin=0,xmax=1,ymin=0,ymax=1,]
	\addplot+[domain=0:1] {x};
\end{axis}
\begin{axis}[xmin=0,xmax=1,ymin=0,ymax=1,hide axis]
	\addplot+[red,domain=0.6:0.8] {x};
\end{axis}
\end{tikzpicture}
\end{document} 
