Absence of Static Phase Separation in the High $T_c$ Cuprate ${\mathrm{Y}\mathrm{B}\mathrm{a}}_2{\mathrm{C}\mathrm{u}}_3{\mathrm{O}}_{6+y}$

We use ${}^{\mathrm{89}}\mathrm{Y}$ NMR in ${\mathrm{Y}\mathrm{B}\mathrm{a}}_2{\mathrm{C}\mathrm{u}}_3{\mathrm{O}}_{6+y}$ in order to evaluate with high sensitivity the distribution of hole content $p$ in the ${\mathrm{C}\mathrm{u}\mathrm{O}}_2$ planes. For $y=1$ and $y=0.6$, this hole doping distribution is found narrow with a full width at half maximum smaller than $\Delta p=0.025$. This rules out any large static phase separation between underdoped and optimally doped regions in contrast with the one observed by STM in Bi2212 and by NQR in LaSrCuO. This establishes that static electronic phase separation is not a generic feature of the cuprates.