  The presence of differential reddening in the direction of Galactic globular
clusters (GCs) has proven to be a serious limitation in the traditional
colour-magnitude diagram (CMD) analysis. Here, we estimate local reddening
variations in the direction of 56 Galactic GCs. To do that, we use the public
catalogs derived as part of the Hubble Space Telescope UV Legacy Survey of
Galactic Globular Clusters, which include photometry in the F275W, F336W,
F438W, F606W, and F814W filters. We correct photometry for differential
reddening finding that for 21 out of 56 GCs the adopted correction procedure
significantly improves the CMDs. Moreover, we measure the reddening law in the
direction of these clusters finding that $R_{V}$ exhibits a high level of
variability within the Galaxy, ranging from $\sim2.0$ to $\sim4.0$. The updated
values of $R_{V}$ have been used to improve the determination of local
reddening variations and derive high-resolution reddening maps in the direction
of the 21 highly-reddened targets within our sample. To compare the results of
the different clusters, we compute the 68$^{\rm th}$ percentile of the
differential-reddening distribution, $\sigma_{\Delta A_{\rm F814W}}$. This
quantity ranges from 0.003 mag to 0.030 mag and exhibits a significant
anti-correlation with the absolute module of the Galactic latitude and a strong
correlation with the average reddening in the direction of each cluster.
Therefore, highly-reddened GCs located in the proximity of the Galactic plane
typically show higher differential-reddening variations across their field of
view.
