What is the ruling on some urine touching the feet during urination; is ghusl (full ritual bath) obligatory, or is it sufficient to remove the urine?

It is obligatory to purify only the spot affected by impurity. So, if urine touches the foot, it is sufficient to purify it by pouring water until the urine is removed. One must perform ghusl (full ritual ablution) from impurity if it afflicts a person and its exact location on the body is unknown.