Inelastic Li6 scattering at 100 MeV/u on C12 and Nb93 has been measured with the high-resolution magnetic spectrometer Grand Raiden. The magnetic-rigidity settings of the spectrometer covered excitation energies from 10 to 40 MeV and scattering angles in the range 0°<θlab.<2°. The isoscalar giant monopole resonance was selectively excited in the present data. Measurements free of instrumental background and the very favorable resonance-to-continuum ratio of Li6 scattering allowed for precise determination of the E0 strengths in C12 and Nb93. It was found that the monopole strength in C12 exhausts 52±3(stat.)±8(sys.)% of the energy-weighted sum rule (EWSR), which is considerably higher than results from previous α-scattering experiments. The monopole strength in Nb93 exhausts 92±4(stat.)±10(sys.)% of the EWSR, and it is consistent with measurements of nuclei with mass number of A≈90. Such comparison indicates that the isoscalar giant monopole resonance distributions in these nuclei are very similar, and no influence due to nuclear structure was observed.